Anemia is common in pregnancy, and increases the risks of adverse pregnancy outcomes including low birth weight. Iron deficiency is a leading cause of anemia in sub-Saharan Africa, and routine iron supplementation has become the standard of care during pregnancy in many countries. However, findings from recent trials among children have raised concerns regarding the safety of iron supplementation in malaria-endemic regions. After a thorough review of the literature, there is limited evidence on the safety and efficacy of prenatal iron supplementation, especially in areas of high malaria burden and among women who are not anemic. In order to address this important research gap, we propose a randomized clinical trial among 1,500 pregnant women in Tanzania. Participants will be randomized to receive 60 milligrams of ferrous sulphate or placebo daily, and will be followed up through the postpartum period. Women who are anemic (defined in Tanzania as Hb<8.5) or iron deficient (ferritin<12 pg/L) will receive iron, as per standard of care, and will not be enrolled in the trial. The primary aims are to determine the safety and efficacy of iron supplementation among pregnant Tanzanian women, as measured by the incidence and density of placental malaria infection, and maternal hemoglobin concentrations and infant birth weight, compared to placebo. Secondary aims are to examine the efficacy of iron supplements on the incidence of maternal anemia, low birth weight, and maternal malaria infection, compared to placebo. Compliance with supplement use will be assessed by direct questioning of women and pill count at monthly clinic visits. Biochemical assessment of compliance will also be assessed measuring the plasma concentration of serum ferritin in a random subsample of 300 women at randomization and at delivery. The study will be conducted as part of a collaboration between the Harvard School of Public Health in Boston, and Muhimbili University of Health and Allied Sciences in Dar es Salaam, Tanzania. PUBLIC HEALTH RELEVANCE: In sub-Saharan Africa, pregnant women are susceptible to anemia and its adverse effects. Any adverse effects of supplemental iron would be of considerable public health importance in malaria-endemic regions of sub-Saharan Africa, due to the high prevalence of iron deficiency and infectious diseases, and the large number of iron supplements that are routinely distributed.